Remove sleep and constant usage warnings

1. It's fine to use `sleep` (by itself) because `sleep` is already being redefined in scope as delegating `Rex::ThreadSafe.sleep` . See https://github.com/rapid7/metasploit-framework/blob/master/lib/rex.rb#L96

2. It's fine to use constants for magic, like you do. The reloading problem disappeared in 1.9, and most people never reload anyway.